In optical communications and optical switching it is well known that signals can be transposed from a first optical signal of a first channel or wavelength to a second optical signal of a second channel or wavelength.
A detector remodulator may be used to convert the first optical signal to the second optical signal and involves the detection of the first signal in which the first (modulated) signal is converted into an electrical signal, followed by the modulation of light of a second (unmodulated) wavelength/channel by the (modulated) electrical signal. Whilst in the electrical domain, the signal may advantageously be processed, for example by one or more of amplification, reshaping, re-timing, and filtering in order to provide a clean signal to be applied to the second wavelength/channel. However, currently in the art, to amplify and filter the electrical signal at high data rates with low noise, the circuitry must be contained in a separate electronic chip, which requires packaging and mounting thereby increasing size and cost and reducing power efficiency.
In U.S. Pat. No. 6,680,791 an integrated chip is provided with a light detector and modulator positioned close together so that the electrical connection between the detector part and the modulator part is short and of low resistivity. However a maximum of only 10 Gb/s data speed is predicted for this structure due to diode capacitance and thin-film resistance limitations [O. Fidaner et al., Optics Express, vol. 14, pp. 361-368, (2006)].
U.S. Pat. No. 6,349,106 describes a tunable laser, driven by a circuit with a signal derived from a first optical wavelength. However because it comprises a III-V-material photonic integrated circuit and involves the use of epitaxial heterostructures and a vertical p-i-n diode structure, is inflexible in its design and therefore inadequate for new applications involving increasing switching speeds, reduced latency, reduced power consumption and the demand for lower cost and high-yield manufacturability. In particular, because the semiconductor devices including the modulator built upon the semiconductor chip are driven by circuits completed between contacts on the top surface and a contact covering all or a large proportion of the base or underside of the chip, the capacitance of the device cannot be readily controlled by design features built into the structures such as doped regions and metal contacts.